Closing Auction Session CAS A Step by Step Guide


Starting August 03, 2026, SEBI is introducing a Closing Auction Session (CAS) for equity shares on which Futures & Options (F&O) contracts are available.


This changes how the closing price is determined and how trading works after 3:15 PM for these eligible shares.


Whether you are a delivery investor, intraday trader or F&O trader, this guide explains what changes, how the new process works, and what it means for your trades.


What is the Closing Auction Session? 


Every trading day, astock has a closing price. This price is important because it is used for activities such as derivatives settlement, index calculation, ETFrebalancingetc. 


Until now, the closing price of eligible shares has been calculated using the Volume Weighted Average Price (VWAP) of trades executed during the last 30 minutes of regular trading. 


Starting August 03, 2026, this will change for equity shares on which Futures & Options (F&O) contracts are available. 


Instead of calculating the closing price from trades executed during the last 30 minutes, the exchange will conduct a Closing Auction Session (CAS) after regular trading ends. During this auction, eligible buy and sell orders are collected and matched to determine a single closing price. 


Does This Apply to All Stocks? 


Not in Phase 1. To ensure a smooth structural transition, the implementation is divided by asset categorization: 


  • F&O Securities: CAS applies exclusively to equity cash segment shares that have active derivative contracts available (e.g., Nifty 50 or highly liquid large-cap counters). Continuous trading for these stocks stops early at 3:15 PM. 

  • Non-F&O Securities: All other cash segment stocks will face no immediate modifications. You can continue trading them via continuous matching all the way until 3:30 PM as you do today. 
 

How does Trading Day change? 


For CAS-eligible shares, the last part of the trading day will now follow a different schedule. 

 

Intraday Square-off Timing from 3 August 2026 
Time
Applicable To 
Remarks
2:45 PM
All Equity & F&O Intraday 
From 2.45 PM all fresh intraday orders and position conversions will be blocked
3:00 PM
Equity Intraday & Equity Cover for CAS Scrips
3.00 PM will be revised Auto Square off time (Moved up from 3:15 PM). 
3:15 PM
A. F&O Intraday & F&O Cover (All Scrips)
B. Equity Intraday & Equity Cover for Non-CAS Scrips
Auto square off will be at 3.15 PM (Unchanged)

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